Various types of rotary machine such as compressors, vacuum pumps, and hydraulic motors or pumps are provided with a rolling piston which rolls against the inside surface of the wall of a cylindrical chamber and which is coupled to a drive shaft via an eccentric portion or crank, which drive shaft is coaxial with said chamber, it being possible in a particular embodiment for the rolling piston to be mounted free to rotate around a drive ring which is itself connected to the crank.
In conventional manner, a separator blade or vane which is slidably mounted in the machine casing divides the empty space around the piston into two variable volume compartments, comprising a low pressure compartment into which a fluid suction port opens out, and a high pressure compartment into which a fluid delivery port opens out.
In normal operation, the separator vane is pressed against the periphery of the rolling piston by a spring interposed between the casing and the vane.
However, it is often desirable to be able to unload or limit the load on the rotary machine.
Proposals have already been made for doing this by means of a clutch for decoupling the machine from its drive member, or by means for clamping the suction port.
In the first case, providing a clutch tends to increase the weight of the machine and also its cost.
In the second case, the need to close the suction port causes considerable power to be absorbed to no purpose and constitutes a loss for which there is no return.
Proposals have also been made in Document FR-A-2 470 267 to remedy these drawbacks by using mechanical stop means for locking the separator vane in a position in which its free edge does not bear against the periphery of the rolling piston, at least during a portion of the motion of the piston. This document proposes providing the stop device in the form of a rod capable of moving in translation perpendicularly to the guide for the separator vane and having formed in the separator vane so as to hold the separator vane off the rolling piston while the rod is in its working position.
However, in practice, such an embodiment is unsatisfactory. In some applications the rolling piston rotates at very high speeds, of the order of several thousand revolutions per minute (rpm). It is therefore particularly difficult to cause a catch or finger that moves particularly to the displacement direction of the vane to penetrate into a notch in the vane oscillating as a function of the position of the rolling piston. Each time the catch enters the receiving notch formed in the vane, the catch suffers from wear as do the walls of the notch, and as a result the lifetime of the device is very limited. Further, on each occasion the catch enters or leaves the notch, the risk of jamming is not negligible. In addition, insofar as the vane can be retracted into a single position only, the prior device is unsuitable for regulating or progressively off-loading the power of the compressor.
The present invention seeks to remedy the above-mentioned drawbacks, and to enable rolling piston rotary machines to be off-loaded or to have their power regulated in a manner which is simple, convenient, and efficient, using a device which is lightweight, robust, and cheap, and absorbing minimum power when off-loaded.
More precisely, an object of the invention is to enable the position of a vane in a rotary machine to be adjusted accurately and reliably while ensuring both a high degree of operating safety and great flexibility in operation.